Kona Stiny Nine Questions

Yo...
I am helping my bro build a kona stinky nine. Actually I thought he was buying a 5" stinky, then he came over with the used frameset and it's a stinky 9. After some consideration, we were both kind of excited about building the nine up & maybe sharing bikes- I can borrow it for whistler & shore trips, he can borrow my XC bike for when he wants something lighter.

Questions-
Whats a good fork for this- would a 170mm marzocchi 66 be enough? Or should I stick it out for a used shiver or triple 8? Keep in mind, we are on a budget and this bike will not be pushed anywhere near its limits, just a whistler vacation bike for DH dabblers.

I've never dealt with a thru-axle rear hub before. The frame came with a hub.... do I need to lace that up, or is there any way to convert a shimano rear hub to fit?

Finally, size. It's a large, 23.7" TT. Kinda big for me, I'm 5'-9". I currently ride a 23" on my FR and 23.5" on my XC bike, both with 70mm stems. Will the large stinky 9 with a 50mm stem be too long for me?